A customer may initiate a voice or data call session over an IP Multimedia Subsystem (IMS) network. The IMS network may then receive and attempt to route the call towards its destination. In order to perform the routing, the network needs to identify a route for the call. The route may be determined based on the domain serving the called party. For example, the IMS network may first make a determination of whether or not a route to the called party is found over the IMS network. If a route is found over the IMS network, then the call is routed over the IMS network. If no route is found over the IMS network, then the call may then be forwarded to a circuit switched network through one or more circuit switched gateway devices, e.g., a border gateway control function, a media gateway control function, and the like.
However, more and more customers are subscribing to multiple services, where some services are provided over an IMS network and others are provided over non-IMS networks. For example, a customer may subscribe to a video share service provided over an IMS network and the customer may also subscribe to a voice service provided over a Global System for Mobile (GSM) communications network. Hence, when a call destined towards a customer who subscribes to both IMS and non-IMS network based services is received, an attempt to locate a route to the called party over the IMS network may still be performed even if the call cannot be successfully completed over the IMS network.